An engine output coupler for a marine stern drive is used to connect an engine flywheel to an output driveshaft in the stern drive so that engine power can be transmitted to the stern drive, and eventually to a propeller. The present invention relates to lubricating the interface of the engine output coupler and the output driveshaft. In particular, the present invention relates to an engine output coupler for a marine stern drive with a semi-sealed lubrication system.
A marine stern drive has a gear case in which a vertical driveshaft drives a horizontal propeller shaft. The vertical driveshaft is driven at the top of the gear case by a universal joint. The output driveshaft, which is driven by the engine output coupler, drives the universal joint. The horizontal propeller shaft is located mostly in a lower torpedo housing. A propeller is mounted on a portion of the horizontal propeller shaft extending rearward from the torpedo housing. The horizontal propeller shaft is rotatably driven at a transmission that interfaces the bottom of the vertical driveshaft and the horizontal propeller shaft.
The output driveshaft extends into a boat through the transom of the boat and is received in the engine output coupler. The output driveshaft has a forward splined end that engages in an axial splined opening of the engine output coupler. It is important that the forward splined end of the output driveshaft can slide in the engine output coupler when the boat is steered or trimmed.
In such a marine stern drive system, spline wear can be a problem due to lack of lubrication, especially when the stern drive is operated continuously at low speeds, such as by commercial fisherman. Periodic lubrication is required to prevent premature spline wear. In U.S. Pat. No. 4,904,214, Eick discloses a system to facilitate relubrication of the splines of an engine output coupler and an output driveshaft. The system in U.S. Pat. No. 4,904,214 also provides grease traps and reservoirs to keep lubricant available to the splines for longer periods of time.
The splines of the driveshaft are normally made of steel, whereas the splines of the coupler are normally made of aluminum. Aluminum is used to battle against corrosion in case a leak develops and allows salt or brackish water to enter into the splined area. Aluminum is not as tough as steel, however, and aluminum splines can strip over time especially if the splined area is not properly lubricated. Although steel splines are tough and more resistent to wear than aluminum splines, it is not usually practical to use steel splines in the coupler because the driveshaft can lock up (i.e. not be able to slide when the boat is steered or trimmed) if the steel splines corrode.